Fiberoptics is the branch of physics concerned with the propagation of light that enters a thread or rod of transparent material at one end and is totally reflected back inward from the wall, thereby being transmitted within the fiber from one end to the other. Fiberoptics is widely applied in medical practice to observe the human body internally. Fiberoptic fibers have also been used to transmit light signals carrying information from both electronic and optical sensors.
In the chemical industry, flow rate measurement is essential in controlling all phases of processing and in determining the material balance for processing units. Once manufactured, the transmission of materials through pipelines between distant places calls for an accurate measurement of flow rate. A multiplicity of techniques is used in this measurement. Flow rate may be determined by measuring the change in pressure caused by either a constriction in a pipe or the insertion of a disk within an orifice into the flow stream. Measuring the impact pressure upon a probe inserted into the process stream will yield the flow rate, as would measuring change in pressure resulting from a change in the direction of this stream. It is also possible to derive the flow rate by measuring the change in the velocity of sound as it passes through the material.
A common flow-rate measuring device is the orifice meter. A plate with a circular orifice at the center is inserted into the process stream, causing the fluid as it passes through the orifice to increase in velocity and correspondingly decrease in pressure. A differential-pressure measuring device measures the fluid pressure just before and just beyond the orifice. Knowledge of this differential pressure allows calculation of the flow rate. This type of flow meter is the most widely used because it is simple and has been long established in plant processes.
One of the most widely used methods is the turbine flow meter. A turbine rotor is allowed to rotate freely in the moving fluid, and its rotation causes a sudden distortion in the field of a small, powerful magnet located in a sensor unit outside the pipe. This distortion generates an alternating-current voltage that is transmitted to a small computer. The computer analyzes this information and calculates and displays the flow rate.
These devices measure the volume-flow rate. This knowledge is useful in monitoring, for instance, the blending of two fluids the density of which are known, such as gasoline and tetraethyllead. In other cases, such as that in which a large quantity of raw material is being transmitted by pipeline and sold by weight, determination of the mass-flow rate is vital. This may be found by adding to a volume flow meter a device that measures the density of the material and calculates mass flow from these two measurements.
There are also flow meters that directly measure mass-flow rate. One of these utilizes two turbines in the flow stream, the first of which, driven at a constant speed, acts as an impeller and imparts a certain velocity to the fluid, depending on the fluid's mass. The second turbine located downstream is adjusted to slow the flow to its original rate; in doing so it receives a torque, or turning force, proportional to the force of the flow (angular momentum). The turbine deflects a spring at an angle proportional to the torque exerted upon it by the fluid. The result is a very accurate and direct measure of the mass flow.
While many systems have been available for the measurement of fluid flow, it is not believed that these systems have usefully incorporated fiberoptics for the transmission of such information. Furthermore, no systems herein before have utilized single optical pathways for the transmission of information to and from the fluid flow being measured. In addition, it is believed that none of the prior art devices have utilized a single optical pathway for the measurement of the rotation of a rotating body, such as a turbine, regardless of the need to measure the fluid flow therein.
It is an object of the present invention to provide an optical flow meter that is inherently safe even in the most hazardous of environments.
It is another object of the present invention to provide a optical flow meter that imparts no electrical disturbances on or about the fluid flow.
It is still another object of the present invention to provide an optical flow meter that is more accurate and reliable than traditional magnetic pickups.
It is still a further object of the present invention to provide an optical flow meter that is adaptable for the measurement of the speed of rotation of a rotating body.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.